Method of increasing the on-stream time of heat transfer units



nite States METHOD OF INCREASING THE ON-STREAM TIME OF HEAT TRANSFERUNITS Italo V. De Chellis, Woodbury, NJ., assignor to Socony Mobil OilCompany, Inc., a corporation of New York No Drawing. Filed Nov. 5, 1956,Ser. No. 620,213 8 Claims. c1. zosso atent a increased octane ratingfrom naphthas and gasolines of lower octane rating than that requiredfor modern high compression, spark-ignited, internal combustion engines,the problem of tube fouling in heat exchangers and furnaces has come tothe fore. It has been found that petroleum fractions which deposit nosediment at ambient temperatures precipitate deposits of unknowncomposition'on. tube surfaces when heated to temperatures of 350 to 1200F. in heat exchangers and furnaces. These deposits are of such magnitudethat designed on-stream periods of, for'example, 180 daysare reduced toas little as 30 to'90 days. a

The nature of the deposit varies with the nature of the fuel and doesnot appear to be correlated with the concentration of a particular typeof material but results from a number of factors among which are theolefin, diolefin, nitrogen, sulfur and oxygen content of the petroleumfraction. V

For evaluating various methods of treating petroleum fractions of theclass defined hereinbefore a tube-wall fraction is heated to 50 0 F.'during passage over the internally heated tube. The tube is weighedbefore and after contact with the selected amount of petroleum fractionbeing tested. The diiference between the weight before and after is ameasure of the on-stream time which heat transfer surfaces in contactwith the selected petroleum fraction can be expected to have.

The test is carried out under conditions such that the petroleumfraction being tested is heated to 500 F. during passage over theinternally heated tube because during the course ofalarge number oftests it was observed that practically all of the deposits are laid downin the 350- 550 F. temperature range. It was also observed that pressureand flow rate have much smaller eifects upon the amount of deposit laiddown than temperature. Therefore, in standard evaluation these two(pressure and rate of flow) were held constant to facilitate bettercontrol and reproducibility of results.

The present method of increasing the on-stream time of heat transfersurfaces in'contact with straight run or cracked petroleum fractionssuch as gasoline, naphtha, gas oil, heating oil, topped crudes and thelike or mixtures of such straight and cracked fractions comprisescontacting the petroleum fraction ofthe class defined hereinbefore withan aqueous'solution of alkali metal salts of organic acids whichsolution is substantially mutually immiscible with an aqueous solutionof alkali metal hydroxide containing at least 29 weight percent alkalimetal hydroxide. The petroleum fraction can be treated at anytemperature above the temperature at which the alkali metal salt of theorganic acid is a solid to temperatures' at which the vapor pressure ofthe constituents deposit testing method was developed. It has beenestablished that the results so obtained arecorrela'ted with plantexperience.

TUBE-WALL DEPOSIT TEST thereof make'the' operation impracticable; Ingeneral,

to an oxygen or sulfur' atom which hydrogenatom'is replaced by an'alkalimetal atom supplied by-an alkali metalhydroxide atambientt'emperaturesinaqiieous-s'olumaterial deposited on the internally heated tubedetermined.

Table I v J [Petroleum traction: straight run Wilmington, Californiagasoline. 40% California coker gasolineJi Treating Mg1ns. Deposit perPercent r Agent Liter ofOil Reduction Percent Treating Agent to Oilin'Tube' Increase "Ratio, 1; Wall Oil-Stream 1bs./b. Un- Treated DepositTime treated 98 0 H 804 2:5 21 18 l4 16 Aque'ous15wt Percent; NaOH 11:5. .121 v 17. 19 24 Aqueous 45 wt. Percent NaOH 1:5. 21 .16 24 3 .32Aqueous 50 wt. Percent KOH 115 21 16 24 32 50 wt. Percent KAP, 19 wt.Percent KOH, 31 wt. I V

Percent H20 1:10 I 7 9 3 5 8 138 l 'lreating temperature, -90" F 'water.

' Fresh blend.

.; KAPpotassiuJn alkyl phenols, KGB-potassium .hyd.ioxide,H,O-

Other petroleum fractions treated in a similar manner showed analogousimprovement as the data in Table II establish.

. Table II Treating agent: a

50 wt. percent KAP 19 wt. percent KOH 31 wt. percent H2O Treatingtemperature F. 80-90 Trfeating ratio: 1 vol. treating agent; 10,vol. orpetroleum rac ron Briefly, the present invention provides for contactingthe petroleum fraction to be heated in contact with heat transfersurfaces, i.e., containing a deposit precursor or precursors. with anaqueous treating solution comprising an alkali metal salt of an organicacid as hereinbefore defined in one ormore stages at a treating agent tooil ratio of about 1 to about 100 volumes of treating agent per volumeof oil to be treated at a temperature above the solidification point ofthe treating agent and below the temperature at which the vapor pressure.of the constituents of the treating agent make the treatmentimpractical. The treated oil is separated from the treating agent,washed with water to remove entrained treating 4 nitrogen. As aconsequence, it is frequently necessary to pretreat naphthas containingamounts of nitrogen in excess of 0.0001 percent. Present practice is tohydrodesulfurize the naphtha to reduce the danger of sulfur poisoningthe platinum catalyst and to reduce corrosion in the reformer hottransfer lines and heat exchangers. To remove nitrogen it is necessarythat the severity of the conditions in the pretreater be increasedappreciably. However, treatment of a naphtha containing 0.0001 percentor more of nitrogen in the manner disclosed herein reduces the load onthe pretreater or eliminates the need for a pretreater as well asincreasing the on-stream time for heat exchangers, furnaces andthe'like.

Similarly, in the hydrocracking of petroleum fractions having an initialboiling point above about 500 F. wherein a petroleum fraction having aninitial boiling point above about 500 F. is heated to a temperatureabove 300 R, and wherein the heated petroleum fraction is 300 F. with atreating agent comprising an aqueous agent solution, and passedto theheating units, i.e., heat V to; the regenerated treating solution'or,preferably, ,by

intimatelymixing the regenerated treating solution with an-aqueonsfortifying solution of alkali metal hydroxide having a concentration ofalkali metal hydroxide such thatfthe regenerated treating solution andthe fortifying solution are substantially immiscible. Afterfortification, the fortified, regenerated treating. solution isseparated from the fortifying alkali metal hydroxide solution. Theseparated fortified, regenerated treating solution is returned to thetreating stage.

Particularly effective, and presently preferred, treating agent is anaqueous mixture of alkali metal hydroxide, alkali metal salt of alkylphenols, i.e., alkali metal alkyl phenolates and water which attemperatures above about 60 F. is substantially immiscible with aqueoussolutions containing at least 29 weight percent alkali metal hydroxide.A suitable aqueous treating agent is one containing about 1 to about 68weight percent alkyl phenols, about 33 to about 39 weight percentpotassium hydroxide and the balance water to make 100 weight-percent. An

alkaline solution containing at least one alkali metal salt of anorganic acid having ahydrogen atom attached to an atom selected from thegroup consisting of, oxygen and sulfur atoms replaceable by an atom ofalkali metal,

said treating agent being substantially immiscible at tempera-turesbelow about 120 F with an aqueous solution consisting of at least 29weight percent alkali metal hydroxide, to obtain treated petroleumfraction and fouled treating agent, separating said treated petroleumfraction from fouled treating agent, and water washing said treatedpetroleum fraction. v

I claim:

1. In the conversion ofa petroleum fraction boiling above 100 F. andcontaining substances'which tend to precipitate and form deposits onheat transfer surfaces when said fraction is heated to temperaturesabove 300 attached to an atom selected from the group consistingadditional,-exemplary treating agent contains at least about 27weightpercent alkali metal isobutyrate, and alkali metal alkylphenolat'e, at least about 25 weight percent alkali metal hydroxide, andthe balance water to make l00'wcight percent in which the ratio ofisobutyrate to alkylphenolate is up to 0.67., t

.. It is interesting to note that extraction of the naphtha to bereformed overnitrogen and olefin sensitive catalysts 1 of oxygen andsulfur which hydrogen atom is replaced by an alkali metal atom suppliedby an alkali metal hydroxide at ambient temperatures in aqueoussolution, to obtain a treated petroleum fraction having a substantiallyreduced concentration of the aforesaid substances which tend toprecipitate and form deposits on heat transfer surfaces when saidfraction is heated to temperatures above 300 F. and fouled treatingagent, separating treated petroleum fraction from fouled treating agent,heating said treated petroleum fraction to a temperature in excess ofabout 300 F., subjecting .said heated treated petroleum fraction to ahydrocarbon conversion, admixing aqueous alkali metal hydroxide solutioncontaining at least 29 weight percent alkali metal hydroxide with theaforesaid separated fouled treating agent to restore the concentrationof free alkali metal hydroxide in the aforesaid treating agent and toobtain a liquid heterogeneous mixture, stratify said liquidheterogeneous mixture, to obtain a liquid fouled treating agent layerand an aqueous alkali metal hydroxide solution, separating said fouledtreating agent, layer with restored concentration of fre alkali metalhydroxide from said aqueous alkali metal hydroxide solution andcontacting further amounts of petroleum fraction boiling above 100 F.and containing substances which tend to precipitate and form deposits onheat transfer surfaces when said fraction is heated to temperaturesabove 300 F. with the aforesaid separated fouled treating agent havingthe restored concentration of free alkali metal hydroxide.

2. The method set forth in claim 1 wherein the separated fouled treatingagent is regenerated with respect to extracted materials whichprecipitate and form deposits when a petroleum fraction containing thesame is heated to temperatures in excess of about 300 F. prior torestoration of the concentration of free alkali metal hydroxide.

3. In the conversion of a normally liquid petroleum fraction containingsubstances which tend to precipitate and form deposits on heat transfersurfaces when said fraction is heated to temperatures above 300 F., theimprovement which comprises contacting said petroleum fraction with atreating agent comprising an aqueous alkaline solution having as itsessential solute an alkali metal salt of at least one organic acidselected from the class consisting of hydroxy aromatic compounds,carboxylic acids, and sulfonic acids which treating agent issubstantially mutually immiscible at temperatures below about 200 F.,with an aqueous solution containing at least about 29 weight percent ofthe hydroxide of said alkali metal to obtain treated petroleum fractionand fouled treating agent containing at least a part of said substances,separating said treated petroleum fraction from said fouled treatingagent, heating said treated petroleum fraction to a temperature inexcess of about 300 F. and subjecting said heated, treated petroleumfraction to a hydrocarbon conversion.

4. The improvement set forth and described in claim 3 wherein the alkalimetal salt of an organic acid is an alkali metal salt of alkyl phenols,the separated treated normally liquid hydrocarbon is water-washed anddried and the fouled treating solution is regenerated, and fortified bycontact with a substantially immiscible aqueous solution of alkali metalhydroxide.

5. In the hydrocracking of petroleum fractions having an initial boilingpoint above about 500 F. wherein a petroleum fraction having an initialboiling point above about 500 F. is heated in heat exchangers andfurnacesv to a temperature above 300 F., and wherein the heatedpetroleum fraction is contacted with a hydrocracking catalyst in thepresence of hydrogen under hydrocracking conditions of temperature andpressure, the improvement which comprises contacting said petroleumfraction prior to heating above 300 F. with a treating agent comprisingan aqueous alkaline solution containing as its essential solute a memberfrom the group consisting of the alkali metal phenolates, alkali metalisobutyrate and mixtures thereof, said treating agent beingsubstantially immiscible at temperatures below about F. with an aqueoussolution consisting essentially of at least 29 weight percent alkalimetal hydroxide, to obtain treated petroleum fraction and fouledtreating agent, separating said treated petroleum fraction from fouledtreating agent and water-washing said treated petroleum fraction.

6. In the reforming of a naphtha which contains impurities from theclass consisting of compounds of sulfur and nitrogen and which tend toform deposits upon heat transfer surfaces when heated above about 300F., wherein said naphtha is preheated to temperatures of about 700-800F., the improvement which comprises contacting said naphtha, prior tosaid preheating step, with a treating agent comprising an aqueoussolution containing potassium hydroxide metal and potassium alkylphenolates, said treating agent being substantially immiscible withaqueous alkaline solutions containing at least 29 weight percent ofalkali metal hydroxide at temperatures below about 200 F. to obtain atreated naphtha and fouled treating agent, and separating said treatednaphtha from fouled treating agent.

7. The improvement in the reforming of naphtha as set forth anddescribed in claim 6 wherein the treated naphtha separated from thefouled treating agent is water-washed, dried, heated to reformingtemperatures and directly contacted with a nitrogen sensitive reformingcatalyst in the presence of hydrogen under reforming conditions oftemperature and pressure.

8. The improvement set forth and described in claim 3 wherein theseparated treated normally liquid hydrocarbon fraction is water-washedand dried and the fouled treating solution is regenerated and theregenerated treating solution is admixed with an aqueous alkali metalhydroxide solution containing more than 29 weight percent alkali metalhydroxide to res-tore the alkali metal hydroxide content of saidtreating solution for reuse.

References Cited in the file of this patent UNITED STATES PATENTS1,859,015 Albright May 17, 1932 2,478,916 Haensel et a1. Aug. 16, 19492,552,399 Browder May 8, 1951 2,585,284 Tom et al. Feb. 12, 19522,771,404 Jezl et a1. Nov. 20, 1956 2,772,220 Bushnell et al Nov. 27,1956

1. IN THE CONVERSION OF A PETROLEUM FRACTION BOILING ABOVE 100*F. ANDCONTAINING SUBSTANCES WHICH TEND TO PRECIPITATE AND FORM DEPOSITS ONHEAT TRANSFER SURFACES WHEN SAID FRACTION IS HEATED TO TEMPERATURESABOVE 300* F., THE IMPROVEMENT WHICH COMPRISES CONTACTING SAID PETROLEUMFRACTION WITH A TREATING AGENT, SAID TREATING AGENT CONSISTING OF ANAQUEOUS ALKALINE SOLUTION OF AT LEAST ONE SALT OF AN ORGANIC ACID ASHEREINAFTER DEFINED WHICH AQUEOUS ALKALINE SOLUTION IS SUBSTANTIALLYIMMISCIBLE WITH AN AQUEOUS SOLUTION OF ALKALI METAL HYDROXIDE CONTAININGAT LEAST 29 WEIGHT PERCENT ALKALI METAL HYDROXIDE AT TEMPERATURES OFABOUT 60*F., SAID ORGANIC ACID BEING AN ORGANIC COMPOUND HAVING AHYDROGEN ATOM ATTACHED TO AN ATOM SELECTED FROM THE GROUP CONSISTING OFOXYGEN AND SULFUR WHICH HYDROGEN ATOM IS REPLACED BY AN ALKALI METALATOM SUPPLIED BY AN ALKALI METAL HYDROXIDE AT AMBIENT TEMPERATURES INAQUEOUS SOLUTION, TO OBTAIN A TREATED PETROLEUM FRACTION HAVING ASUBSTANTIALLY REDUCED CONCENTRATION OF THE AFORESAID SUBSTANCES WHICHTEND TO PRECIPITATE AND FORM DEPOSITS ON HEAT TRANSFER SURFACES WHENSAID FRACTION IS HEATED TO TEMPERATURES ABOVE 300*F. AND FOULED TREATINGAGENT, SEPARATING TREATED PETROLEUM FRACTION FROM FOULDED TREATINGAGENT, HEATING SAID TREATED PETROLEUM FRACTION TO A TEMPERATURE INEXCESS OF ABOUT 300*F., SUBJECTING SAID HEATED TREATED PETROLEUMFRACTION TO A HYDROCARBON CONVERSION, ADMIXING AQUEOUS ALKALI METALHYDROXIDE SOLUTION CONTAINING AT LEAST 29 WEIGHT PERCENT ALKALI METALHYDROXIDE IN THE AFORESAID SEPARATED FOULDED TREATING AGENT TO RESTORETHE CONCENTRATION OF FREE ALKALI METAL HYDROXIDE IN THE AFORESAIDTREATING AGENT AND TO OBTAIN A LIQUID HETEROGENEOUS MIXTURE, STRATIFYSAID LIQUID HETEROGENEOUS MIXTURE, TO OBTAIN A LIQUID FOULED TREATINGAGENT LAYER AND AN AQUEOUS ALKALI METAL HYDROXIDE SOLUTION, SEPARATINGSAID FOULED TREATING AGENT LAYER WITH RESTORED CONCENTRATION OF FREEALKALI METAL HYDROXIDE FROM SAID AQUEOUS ALKALI METAL HYDROXIDE SOLUTIONAND CONTACTING FURTHER AMOUNTS OF PETROLEUM FRACTION BOILING ABOVE100*F. AND CONTAINING SUBSTANCES WHICH TEND TO PRECIPITATE AND FORMDEPOSITS ON HEAT TRANSFER SURFACES WHEN SAID FRACTION IS HEATED TOTEMPERATURES ABOVE 300*F. WITH THE AFORESAID SEPARATED FOULED TREATINGAGENT HAVING THE RESTORED CONCENTRATION OF THE FREE ALKALI METALHYDROXIDE.